The present invention relates to hearing aids, and more particularly to a recharging system for an in-the-ear rechargeable hearing aid. Such rechargeable hearing aid system eliminates the burden of replacing the hearing aid battery, and thus provides significant advantages to the elderly and others with impaired eyesight or reduced manual dexterity.
Known hearing aids utilize very small non-rechargeable batteries for their power source. Various in-the-ear hearing aids have been developed that provide both good performance and are less visible than traditional behind-the-ear hearing aids. Versions of in-the-ear hearing aids are known that are entirely in the ear canal, mostly within the ear canal, and only partially within the ear canal. In spite of their differences, all of these in-the-ear hearing aids share the requirement for a very small battery.
The need for a small battery for hearing aids has been met using known zinc air batteries. The zinc air batteries are inexpensive and have a useful life up to several days. However, the very small size that makes the zinc air batteries practical for a small hearing aid also make the batteries difficult to handle. Hearing aid users with poor eyesight or reduced manual dexterity have difficulty replacing the zinc air batteries. Both of these infirmities are associated with advanced age, and are likely to be found in hearing air users. Additionally, there is a risk of dropping and damaging the hearing aid when changing the batteries.
The disposable batteries are considered dangerous if swallowed, and therefore the ingestion of such batteries presents a health risk. There is therefore a risk of small children or infants swallowing the small hearing aid batteries, thereby requiring careful storage of new batteries, and immediate disposal of used batteries. Additionally, due to their size and shape, the batteries can be mistaken for pills, which pills are also common place with those of advanced age who frequently have diminished vision.
The chemicals used in replaceable batteries are often classified as being a toxic material. As society becomes increasingly more protective of the environment, the cost of disposing or recycling batteries will rise, and be a further deterrent to the use of disposable batteries.
One reason for the development of miniature hearing aids is to reduce the unsightly appearance of the device in the patient""s ear. However, the flap covering the replaceable battery in known hearing aids is on the surface of the hearing aid that is visible when the hearing aid is inserted into the ear canal, and draws the attention that the miniature hearing aid was developed to avoid.
A rechargeable hearing aid is described in U.S. Pat. No. 5,610,494 for xe2x80x9cDevice for Recharging the Storage Battery of an Intra-auricular Prosthesis and Method for Manufacturing Same,xe2x80x9d issued Mar. 11, 1997. While the ""494 patent addresses the issues raised here, it does not provide the best solution. The ""494 patent teaches a recharging system requiring contacts on the exterior of the intra-auricular prosthesis (i.e., hearing aid), and a charger comprising a box with recesses matching the shape of the hearing aid, which recesses contain electrical contact which cooperate with the contacts on the hearing aid. A device according to the ""494 patent therefore requires that the hearing aid be carefully positioned in the recharging device. Such positioning requirement duplicates one of the problems the ""494 patent is intended to solve because the hearing aid must be placed precisely in the correct position to line up the contacts. Due to the soft structure of a hearing aid, such positioning may be difficult for those with vision problems or reduced manual dexterity. There is also a requirement to keep the contacts clean. Due to the low voltage nature of the charging circuit, even small resistance may impact charging performance. Such inefficiencies in charging are especially costly when the recharger is itself a portable battery powered recharger. The ""494 patent also teaches that recharging could be accomplished using an inductive charger, but that a large coil would be required in the hearing aid that would unacceptably increase the bulk of the hearing aid. The ""494 patent is incorporated herein by reference.
What is therefore needed is a rechargeable hearing aid that can be recharged without removing the battery, and which recharging may be performed without precise placement of the hearing aid within a charging device.
The present invention addresses the above and other needs by providing a rechargeable hearing aid that is recharged by placing the hearing aid in an inductive charging reservoir. Power for recharging the hearing aid battery is provided through inductive coupling of a primary coil in a charging reservoir and a secondary coil in the hearing aid. The inductive power transmission requires only a general alignment of the hearing aid with the charging reservoir. In a preferred embodiment, a lithium ion battery is used in the rechargeable hearing aid because of the energy density of the lithium ion battery and capacity for a very large number of recharges.
In accordance with one aspect of the invention, there is provided a rechargeable hearing aid that permits recharging the hearing aid battery without removing the battery from the hearing aid. Many hearing aid users are advanced in years and suffer from a loss of sight and/or manual dexterity. Such individuals often find it difficult to perform the manipulation required to replace a very small battery in a small device. The cumbersome task of removing a very small battery from a small device is replaced by simply placing the entire hearing aid in a charging reservoir.
It is also a feature of the present invention to eliminate the hazards resulting from the use of disposable batteries. For example, batteries are known to contain toxic substances, and are dangerous if swallowed. A typical hearing aid battery is similar in size and shape to common pills. A hearing aid user with poor eyesight may easily mistake a used battery for a pill, and swallow the battery. The disposable batteries are also a hazard to children who may place the batteries in their mouths. Additionally, there are also environmental costs surrounding the disposal of used batteries due to the toxic content of the batteries. Advantageously, rechargeable hearing aids avoid all of these hazards.
It is a further feature of the invention to recharge the hearing aid battery inductively. The present invention provides power required for recharging using inductive coupling between a primary coil in a charging reservoir, and a secondary coil in a hearing aid. Inductive charging advantageously eliminates the need for contacts on the exterior of the hearing aid, which contacts are required for non-inductive charging of the battery, and which contacts may become soiled, thus impairing their conductivity. Inductive charging further eliminates the requirement to precisely align hearing aid contacts with recharger contacts, which alignment is difficult for a hearing aid user with poor sight or poor manual dexterity.
It is an additional feature of the invention to eliminate the need to provide access for replacement of a disposable battery. The requirement to regularly replace the disposable battery creates a requirement that the battery be easily accessible. In known Completely-In-the-Canal (CIC) hearing aids, the disposable battery is removable through a door in the end of the hearing aid facing away from the ear drum, and the battery is located just inside the door. The placement of the battery in this location interferers with placement of the hearing aid""s microphone. The placement of a rechargeable battery within the hearing aid allows the hearing aid designer to optimally select and locate the microphone. Additionally, the battery door in known CIC hearing aids is visible when the hearing aid is in the user""s ear canal, thus reducing the cosmetic value of a CIC hearing aid. The use of a rechargeable battery eliminates the requirement for the unsightly door.